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Pop quiz: If you push on light, does it push back?
If you are dust, then the answer is as clear as a Hubble Space Telescope image.
More than a century after it was first discovered with a 3-foot (1-meter) ground telescope, a cloud of interstellar dust has been photographed in fine detail by Hubble. The picture reveals a strange phenomenon, where the light from a star bullies small bits of space dust, separating them from the larger particles with which they travel.
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The radial streaks of light coming out of the upper right are artifacts, caused when the starlight strikes Hubble's lens. But the parallel streaks, racing from the lower left to the upper right, are real.
IMAGE: NASA/STScI/AURA
Zoom in to the Pleiades with our cool animation! |
The cloud, called Barnard's Merope Nebula after its discoverer, E.E. Barnard, does not produce any light of its own, but instead reflects light from a nearby star named Merope. The Hubble image reveals for the first time parallel streaks in the nebula, running from the lower left to the upper right in the new image.
The streaks are caused when the nebula's dust particles slam into the particles of starlight, called photons, said University of Hawaii astronomer George Herbig, who produced the image along with colleague Theodore Simon.
The phenomenon is called radiation pressure.
The nebula, filled with dust particles of different sizes, is drifting past the star at a relative speed of about 6.8 miles (11 kilometers) per second.
"Radiation pressure is rather like a terrestrial wind, Herbig explains. "The photons carry momentum, which they transfer to the dust on impact."
The photons have a greater effect on the smaller dust particles, which have less mass and are slowed down more than the larger particles. The nearly straight lines pointing toward the star, which is out of view in the upper right, are the streams of larger particles still zooming toward the star. Smaller particles have been left behind, in the image's lower left.
| Did You Know? |
| Nebula= cloud
"Nebula" is Latin for cloud. A nebula is made up mostly of hydrogen, but also contains traces of water and alcohol, and many other compounds. See one that looks like an eye. Celestial bar codes
Most photographs made by large telescopes are not what they appear to be. Learn about "reflection nebulae" and how you can understand the colors. Hubble, Hubble, and more Hubble!
Browse hundreds of space images, Hubble and otherwise, in our photo galleries.
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"Imagine that you have a handful of dust of all sizes, from sand-grain sizes down to the finest talcum powder," Herbig said. "If you throw that handful up into a strong wind, the big grains will not be carried very far before they fall back, while the finest stuff will be carried a long way."
Barnard's Merope Nebula is bright, scientists say, because it is only about 0.06 light-years from Merope -- about 3,500 times the distance from Earth to the Sun. (A light-year is the distance light travels in a vacuum in one year, about 5.88 trillion miles or 9.46 trillion kilometers.) The nebula will move past the star over the next few thousand years, if it is not destroyed in the process.
The nebula and the star are in the Pleiades star cluster, easily visible to the naked eye on a clear winter evening.
The small grouping of bright blue stars is named after the "Seven Sisters" of Greek mythology. Resembling a small dipper, this star cluster lies in the constellation Taurus, about 380 light-years from Earth. The unaided eye can spot a half a dozen bright stars in the cluster, but a small telescope will reveal that the Pleiades contains many hundreds of fainter stars.
Click here for more news and information about nebula and other deep-sky objects.
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